Ionic Exchange Resins
Ionic exchange resins are known. Most modern ionic exchange resins, or ionic exchangers, consist of a synthetic polymer backbone or matrix to which is attached a functional group that gives each ionic exchanger its specific properties. Ionic exchange resins are produced in various physical forms depending on the end use for the resin. Most commonly, they are used as small spherical beads or granules, but they can be made into membranes, fibers, tubes, cloth, or foams. By special manufacturing techniques, the polymers, especially in the bead form, may be made with porous structures instead of the conventional solid gel resin structure. Such resins are called macroporous or macroreticular resins.
The functional groups that are distributed throughout the resin structure contain fixed electric charges or ion-active groups, each of which is associated with a mobile counter ion of opposite charge. These mobile ions are capable of reacting with or exchanging with other ions of like sign when they are in contact with a solution containing such ions. It is important that ionic exchange resins swell to a certain extent in aqueous or liquid solution so that the solution can diffuse into the resin and come into contact with the active sites.
When the fixed electrical charges within the resin matrix are negative (when the fixed functional group is a sulfonic group, for example), the mobile ions are cations and the resin is said to be a cationic exchange resin. Conversely when the fixed groups are positively charged, the mobile ions are anions and the resin is an anionic exchanger.
The polymer matrices are usually cross-linked to make them insoluble and to give them mechanical strength and stability. The extent of cross-linking must be controlled so as to give good mechanical properties to the resin while permitting enough water absorption and swelling to ensure good ionic exchange activity.
Ionic exchange has been defined as the reversible interchange of ions between a solid and a liquid phase in which there is no permanent change in the structure of the solid. This means that ionic exchangers are not consumed by ordinary usage, but when they are exhausted, they can be regenerated or reconverted to their original state and reused. Ionic exchange is regarded as a unit process in chemical engineering and it has many applications. One of the best known and largest applications is water softening, in which calcium and magnesium ions, which cause water hardness, are removed from the water and exchanged for sodium ions from the resin. When the resin is exhausted, it is brought back to its original state by treatment with a sodium chloride solution. By a more complex process, water may be not only softened, but completely deionized. Ionic exchange resins are widely used to treat boiler feed water, process water, and to perform a large number of separations and reactions in the manufacture of chemicals, foods, pharmaceuticals, electronic devices, and many other products.
Ionic exchange is a widespread phenomenon in nature, occurring in living cells and in soils, for example. Ionic exchange materials include silicates, phosphates, fluorides, humus, wool, proteins, cellulose, alumina, glass, and many others. The first industrial ionic exchangers were probably inorganic aluminum silicates, used for softening water and treating sugar solutions. Later on, it was discovered that sulfonated coal is a relatively effective ionic exchange material, but such materials are fragile and are useful only under restricted operating conditions. In the United States nearly all ionic exchange applications use synthetic polymer resins.
Nitric Oxide
At room temperature nitric oxide (NO) is a gas that can participate in many chemical reactions. There are many known biological and medical uses of NO. A nonlimiting list of some of these uses include:
Blood Flow: NO relaxes the smooth muscle in the walls of the arterioles. At the time of each systole, the endothelial cells that line the blood vessels release a puff of NO. This diffuses into the underlying smooth muscle cells causing them to relax and thus permit a surge of blood to pass through easily.
Nitroglycerine, which is often prescribed to reduce the pain of angina, does so by generating nitric oxide, which relaxes the walls of the coronary arteries and arterioles.
NO also inhibits the aggregation of platelets and thus keeps inappropriate clotting from interfering with blood flow.
Kidney Function: Release of NO around the glomeruli of the kidneys increases blood flow through them thus increasing the rate of filtration and urine formation.
Penile Erection: The erection of the penis during sexual excitation is mediated by NO released from nerve endings close to the blood vessels of the penis. Relaxation of these vessels causes blood to pool in the blood sinuses producing an erection.
The popular prescription drug sildenafil citrate inhibits the breakdown of NO and thus enhances its effect.
Peristalsis: The wavelike motions of the gastrointestinal tract are aided by the relaxing effect of NO on the smooth muscle in its walls.
Because of the many well-known uses of NO, there is therefore a need in the art for additional methods directed to NO production and its delivery at target locations.